An alternating-current surface-discharge panel representative of a plasma display panel (hereinafter abbreviated as “panel”) has a large number of discharge cells formed between the front plate and the rear plate faced to each other. For the front plate, a plurality of display electrode pairs, each made of a scan electrode and a sustain electrode, are formed on a front glass substrate in parallel with each other. A dielectric layer and a protective layer are formed to cover these display electrode pairs. For the rear plate, a plurality of parallel data electrodes are formed on a rear glass substrate and a dielectric layer is formed over the data electrodes to cover them. Further, a plurality of barrier ribs are formed on the dielectric layer in parallel with the data electrodes. Phosphor layers are formed over the surface of the dielectric layer and the side faces of the barrier ribs. Then, the front plate and the rear plate are faced to each other and sealed together so that the display electrode pairs are intersected with the data electrodes. A discharge gas containing xenon in a partial pressure ratio of 5%, for example, is charged into the inside discharge space formed between the plates. Discharge cells are formed in portions where the respective display electrode pairs are faced to the corresponding data electrodes. For a panel structured as above, gas discharge generates ultraviolet light in each discharge cell. This ultraviolet light excites the red (R), green (G), and blue (G) phosphors so that the phosphors emit the respective colors for color display.
A general method of driving a panel is a subfield method: one field is divided into a plurality of subfields and combinations of light-emitting subfields provide gradation display.
Each subfield has an initializing period, an address period, and a sustain period. In the initializing period, initializing discharge is caused so that wall charge necessary for the succeeding address operation is formed on the respective electrodes and priming particles (excited particles to work as priming for discharge) are generated to stabilize the address discharge.
In the address period, application of address pulse voltage selectively to the discharge cells to be lit causes address discharge and forms wall charge (hereinafter this operation also being referred to as “addressing”). In the sustain period, sustain pulses are applied alternately to the display electrode pairs, each made of a scan electrode and a sustain electrode. This application causes sustain discharge in the discharge cells having generated the address discharge, and causes the phosphor layers of the corresponding discharge cells to emit light. Thus, an image is displayed.
Further, a novel driving method is disclosed among the subfield methods. In this driving method, initializing discharge is caused by using a gently changing voltage waveform, and initializing discharge is further performed selectively on the discharge cells having generated sustain discharge. Thus, light emission unrelated to gradation display is minimized and the contrast ratio is improved.
Specifically, among a plurality of subfields, in the initializing period of one subfield, an initializing operation for causing initializing discharge in all the discharge cells (hereinafter abbreviated as “all-cell initializing operation”) is performed. In the initializing period of each of the other subfields, an initializing operation for causing initializing discharge only in the discharge cells having generated sustain discharge (hereinafter “selective initializing operation”) is performed. In this driving method, the light emission unrelated to image display is only the light emission caused by the discharge in the all-cell initializing operation and thus the luminance of the areas displaying black pictures (hereinafter “black picture level”) is only due to the weak light emission in the all-cell initializing operation. Thus, images having a high contrast can be displayed. (See Patent Document 1, for example.)
Further, the above Patent Document 1 includes the description of so-called erasing discharge using a narrow pulse. In this erasing discharge, the pulse width of the last sustain pulse in the sustain period is set shorter than the pulse widths of the other sustain pulses so that the potential difference between the display electrode pairs caused by the wall charge thereon is alleviated. Generating this erasing discharge using a narrow pulse can ensure the address operation in the address period of the succeeding subfield and provide a plasma display device having a high contrast ratio.
Further, techniques are proposed to control the luminance of an image to be displayed and thus to improve the visibility of the image. One of such techniques is to detect the average picture level (hereinafter “APL”) of input image signals and to control the number of sustain pulses in the sustain period according to the APL. (See Patent Document 2, for example.)
The number of sustain pulses in each subfield is determined by multiplying a ratio of the brightness to be displayed (hereinafter “brightness weight”) in the subfield by a proportionality factor (hereinafter “luminance factor”). In this technique, the luminance factor is controlled according to the APL, and thereby the number of sustain pulses in each subfield is determined. Control is made so that the luminance factor is lower for an image signal having a higher APL, and the luminance factor is higher for an image signal providing a dark image and having a lower APL. Such control can increase the luminance of the image to be displayed and make the dark image brighter, and thus provides a more visible image, when the APL is lower.
Immediately after a plasma display device is powered on, the operation of each circuit, such as an image signal processing circuit, power supply circuit, and driving circuit, is not stable and thus an abnormal image can be displayed in the plasma display device. A general method of addressing this problem is to stop the address operation and display a black picture on the entire display surface (hereinafter “image muting”) for a few seconds immediately after the power-on until the stabilized operation of each circuit.
On the other hand, in the panel of a plasma display device immediately after the driving has been initiated by the power-on, insufficient priming particles can induce strong discharge in the initializing operation. This strong discharge can cause some discharge cells to generate sustain discharge and emit light even though address operation is not performed therein (hereinafter referred to as “initializing spot”).
Particularly in the muting period, a black picture is shown on the entire image display surface of the panel. Thus, the initializing spots are easy to recognize and the quality of displayed images seems to deteriorate.    [Patent Document 1] Japanese Patent Unexamined Publication No.    [Patent Document 2] Japanese Patent Unexamined Publication No. H11-231825